• Title, Summary, Keyword: stars: formation

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COSMIC RAYS AND GAMMA-RAYS IN LARGE-SCALE STRUCTURE

  • INOUE SUSUMU;NAGASHIMA MASAHIRO;SUZUKI TAKERU K.;AOKI WAKO
    • Journal of The Korean Astronomical Society
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    • v.37 no.5
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    • pp.447-454
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    • 2004
  • During the hierarchical formation of large scale structure in the universe, the progressive collapse and merging of dark matter should inevitably drive shocks into the gas, with nonthermal particle acceleration as a natural consequence. Two topics in this regard are discussed, emphasizing what important things nonthermal phenomena may tell us about the structure formation (SF) process itself. 1. Inverse Compton gamma-rays from large scale SF shocks and non-gravitational effects, and the implications for probing the warm-hot intergalactic medium. We utilize a semi-analytic approach based on Monte Carlo merger trees that treats both merger and accretion shocks self-consistently. 2. Production of $^6Li$ by cosmic rays from SF shocks in the early Galaxy, and the implications for probing Galaxy formation and uncertain physics on sub-Galactic scales. Our new observations of metal-poor halo stars with the Subaru High Dispersion Spectrograph are highlighted.

Initial Mass Function and Star Formation History in the Small Magellanic Cloud

  • Lee, Ki-Won
    • Journal of the Korean earth science society
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    • v.35 no.5
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    • pp.362-374
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    • 2014
  • This study investigated the initial mass function (IMF) and star formation history of high-mass stars in the Small Magellanic Cloud (SMC) using a population synthesis technique. We used the photometric survey catalog of Lee (2013) as the observable quantities and compare them with those of synthetic populations based on Bayesian inference. For the IMF slope (${\Gamma}$) range of -1.1 to -3.5 with steps of 0.1, five types of star formation models were tested: 1) continuous; 2) single burst at 10 Myr; 3) single burst at 60 Myr; 4) double bursts at those epochs; and 5) a complex hybrid model. In this study, a total of 125 models were tested. Based on the model calculations, it was found that the continuous model could simulate the high-mass stars of the SMC and that its IMF slope was -1.6 which is slightly steeper than Salpeter's IMF, i.e., ${\Gamma}=-1.35$.

Spatial distrbibution of star formation in extremely strong $H{\alpha}$ emitters

  • Shim, Hyunjin;Chary, Ranga Ram
    • The Bulletin of The Korean Astronomical Society
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    • v.39 no.2
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    • pp.65.1-65.1
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    • 2014
  • We present Palomar/SWIFT integral field spectroscopy of z~0.2 strong $H{\alpha}$ emitters identified in the Sloan Digital Sky Survey. The large Halpha equivalent widths as well as the huge specific star formation rates of these galaxies are comparable with that of z>4 Lyman break galaxies, thus understanding the gas kinematics and the distribution of massive stars in these systems will help to obtain a better understanding of high-redshift star forming environments and the growth of massive galaxies. We measure the velocity dispersion across the entire galaxy, estimate the number density and the spatial distribution of massive stars from the emission line morphologies. The role of minor mergers in powering star formation is investigated as an alternative to cold flow driven star formation.

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The rise and fall of dusty star formation in (proto-)clusters

  • Lee, Kyung-Soo
    • The Bulletin of The Korean Astronomical Society
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    • v.44 no.2
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    • pp.38.1-38.1
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    • 2019
  • The formation and evolution of galaxies is known to be fundamentally linked to the local environment in which they reside. In the highest-density cluster environments, galaxies tend to be more massive, have lower star formation rates and dust content, and a higher fraction have elliptical morphologies. The stellar populations of these cluster galaxies are older implying that they formed the bulk of their stars much earlier and have since evolved passively. Quantifying the specific environmental factors that contribute to shaping cluster galaxies over the Hubble time and measuring their early evolution can only be accomplished by directly tracing the galaxy growth in young clusters and forming porto-clusters. In this talk, I will present a novel technique designed to map out the total dust obscured star formation relative to where existing stars lie. I will demonstrate that this technique can be used 1) to determine if/where/when the activity is heightened or suppressed in dense cluster environment; 2) to measure the total mass and spatial distribution of stellar populations; and 3) to better inform theoretical models. Our ongoing work to extend this analysis out to protoclusters (z~2-4) will be discussed.

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A NEAR-INFRARED STUDY OF THE HIGHLY-OBSCURED ACTIVE STAR-FORMING REGION W51B

  • Kim, Hyo-Sun;Nakajima, Yasushi;Sung, Hwan-Kyung;Moon, Dae-Sik;Koo, Bon-Chul
    • Journal of The Korean Astronomical Society
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    • v.40 no.1
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    • pp.17-28
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    • 2007
  • We present wide-field $JHK_s$-band photometric observations of the three compact H II regions G48.9-0.3, G49.0-0.3, and G49.2-0.3 in the active star-forming region W51B. The star clusters inside the three compact H II regions show the excess number of stars in the $J-K_s$ histograms compared with reference fields. While the mean color excess ratio $(E_{J-H}/E_{H-K_s})$ of the three compact H II regions are similar to ${\sim}2.07$, the visual extinctions toward them are somewhat different: ${\sim}17$ mag for G48.9-0.3 and G49.0-0.3; ${\sim}23$ mag for G49.2-0.3. Based on their sizes and brightnesses, we suggest that the age of each compact H II region is ${\leq}2\;Myr$. The inferred total stellar mass, ${\sim}1.4{\times}10^4M_{\odot}$, of W51B makes it one of the most active star forming regions in the Galaxy with the star formation efficiency of ${\sim}10%$.

FIR VIEW OF DISKS OF WEAK-LINE T TAURI STARS

  • Takita, Satoshi;Doi, Yasuo;Arimatsu, Ko;Ootsubo, Takafumi;AKARI Team
    • Publications of The Korean Astronomical Society
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    • v.32 no.1
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    • pp.127-129
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    • 2017
  • We have observed ~60 Weak-line T Tauri stars (WTTSs) toward the Chamaeleon star forming region using the AKARI Far-Infrared Surveyor (FIS) All-Sky maps. We could not detect any significant emission from each source even at the most sensitive WIDE-S band. Then, we have performed stacking analysis of these WTTSs using the WIDE-S band images to improve the sensitivity. However, we could not detect any significant emission in the resultant image with a noise level of $0.05MJy\;sr^{-1}$, or 3 mJy for a point source. The three-sigma upper limit of 9 mJy leads to the disk dust mass of $0.01M_{\oplus}$. This result suggests that the disks around Chamaeleon WTTSs are already evolved to debris disks.

Tidal Stripping Substructure on Spatial Distribution of Stars in Several Globular Clusters from UKIRT Observation

  • Sohn, Young-Jong;Chun, Sang-Hyun;Kang, Minhee
    • The Bulletin of The Korean Astronomical Society
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    • v.38 no.2
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    • pp.78.1-78.1
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    • 2013
  • The hierarchical model of galaxy formation predicts that galaxy halos contain merger relics in the form of long stellar stream. Thus, tidal substructure of stars around globular clusters, such as tidal tails, could be an essential evidence of the merging scenario in the formation of the Galaxy. From April 2010 to December 2012, we obtained $45^{\prime}{\times}45^{\prime}$ wide-field JHKs near-infrared photometric imaging data for about 20 globular clusters in the Milky Way, and examined the stellar density distribution around globular clusters. Here, we introduce the preliminary results of stellar spatial distributions and radial surface density profiles of four globular clusters. In order to minimize the field star contamination and identify the cluster's member candidates stars, we used a statistical filtering algorithm and gave weights on the CMDs of globular clusters. In two-dimensional stellar density maps, we could found tidal stripping structures for some globular clusters. The orientation of tidal substructure seems to associate with the effects of dynamical interactions with the Galaxy and cluster's orbit. Indeed, the radial surface density profile accurately describes this stripping structures as a break in the slope of profile. The observational results could give us further observational evidence of merging scenario of the formation of the Galaxy.

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